A group of disorders marked by progressive degeneration of motor neurons in the spinal cord resulting in weakness and muscular atrophy, usually without evidence of injury to the corticospinal tracts. Diseases in this category include werdnig-hoffmann disease and later onset spinal muscular atrophies of childhood, most of which are hereditary. (Adams et al., Principles of Neurology, 6th ed, p1089)

An inherited disorder characterized by degeneration of the spinal cord and the cerebellum. Symptoms may appear at any age and include progressive loss of coordination of gait, hands, speech, and eye movements.

Spinal muscular atrophy (sma) is a genetic disease that attacks nerve cells, called motor neurons, in your spinal cord. These neurons communicate with your voluntary muscles - the ones you can control, like in your arms and legs. As you lose the neurons, your muscles weaken. This can affect walking, crawling, breathing, swallowing and head and neck control.sma runs in families. Parents usually have no symptoms, but still carry the gene. Genetic counseling is important if the disease runs in your family.there are many types of sma, and some of them are fatal. Life expectancy depends on the type you have and how it affects your breathing. There is no cure. Medicines and physical therapy help treat symptoms.